This invention relates to a program reading apparatus for reading a program on a program carrier, which has a movable reading head adapted to scan the program carrier on the apparatus.
In a knitting machine having an electromechanical patterning mechnism, a program reading apparatus is provided for reading design instructions on a design paper or program carrier to produce electric signals for controlling the patterning mechanism. A program reading apparatus, especially for a home knitting machine, may be constructed, for economy, such that it includes a single movable reading head adapted to scan the program carrier along a predetermined scanning line and which is intermittently fed, step by step, transversely to the scanning line on the apparatus. Such a program reading apparatus is disclosed in U.S. Patent Application Ser. No. 737,433, titled "Knitting Machine Coupled With The Program Reading Device", filed on Nov. 1, 1976, now U.S. Pat. No. 4,085,597.
In order to attain high mechanical speed capability and response in scanning, a program reading apparatus preferably employs an electric linear motor for moving the reading head along the scanning path. The reading head is usually initially positioned at its starting position at one end of the scanning path to read an instruction specially provided on a predetermined portion of the program carrier appropriately positioned relative to the starting position for the head. The control circuit controlling the linear motor then causes the reading head to move from the starting position to the other stroke end of the scanning path and thereafter, to return to the starting position. Upon each arrival of the reading head to the starting position. Upon each arrival of the reading head to the starting position, however, the reading head in a conventional machine may be rebounded, thereby moving to a position in which it begins to read design instructions within the design region of the program carrier. Subsequent starting of scanning movement of the reading head from such position will, inevitably, cause misreading of such design instructions on the program carrier along the scanning line, thereby resulting in improper operation of the knitting machine.
To ensure proper positioning of the reading head at the correct starting position at the beginning of each scan, the control circuit may be implemented to energize the linear motor to urge the reading head to the starting position for an additional period of time sufficient for the head to become stationary after it has first arrived at or returned to the starting position. Such an implementation, however, is disadvantageous in that a relatively long period of time is thereby required for a complete scan cycle because of such additional required period of time. As a result, the rapidity with which a scanning cycle may be effected is considerably impaired.